1. Field of the Invention
The invention relates to a valving apparatus for connection between a tubular work string and a downhole well tool having a fluid pressure expandable packing element.
2. Description of the Prior Art
There are many downhole tools which incorporate fluid pressure actuated expandable packing elements which are expanded into sealing engagement with the wall of the casing through the application of fluid pressure through the bore of an interconnected tubular work string. When the fluid level in the well is sufficiently high that the hydrostatic pressure existing in the casing annulus is substantially equal to the hydrostatic pressure represented by the column of fluid contained in the interconnected work string and tool, then no problems are encountered in the direct application of fluid pressure to the expandable packing element of the tool. On the other hand, in wells having a low fluid level, the hydrostatic pressure existing in the casing annulus at the time that it is desired to release the expandable packing element from engagement with the casing wall, may often be substantially less than the hydrostatic pressure existing in the interconnected work string and the central bore of the tool. Under these circumstances, it is impossible to effect the contraction of the expandable packing elements since they are subject to the aforementioned pressure differential and maintained by such pressure differential in their expanded position.
The prior art is devoid of a simple, reliable apparatus for effecting the supply of fluid pressure through the bore of a tool to effect the expansion of a fluid pressure actuated packing element, and at the same time, when such pressure is released, to effect the equalization of pressure between the bore of the tool and the casing annulus to permit the expandable packing elements to retract to their normal run-in positions, free of engagement with the casing wall.